Rotating rigid disc magnetic storage devices typically use data transducers that fly on an air cushion immediately adjacent to the storage surface. The transducer is held just above the surface by an air bearing effect. This technique, widely used in presently known disc drives, is typically used in what is referred to as a Winchester disc drive.
In a Winchester disc drive, the data transducers are supported by a carriage assembly that is controllably driven to position the transducer at a predetermined landing zone on the disc storage surface when the drive is not in use. In some cases, the landing zone is located inside the innermost annular data storage track of the storage surface. In some cases, the driving mechanism may be a linear translator such as a linear voice coil solenoid. In other cases, the driver may be a stepper motor or a rotary actuator. When power is removed, the driver becomes disenabled and the back EMF of the stepper motor is used to move the transducers to the landing zone.
The disc storage surface is typically coated with very thin magnetic material which stores the recorded data for later retrieval and/or replacement. The storage surface is packed with very high data densities on the order of 10,000 bits or more per inch. The storage surface is particularly sensitive to being damaged. Any minute scratch or indentation may deform the storage surface with resultant loss of data and data storage capability at the damaged site.
The movement of a data transducer across the recording surface in the absence of the air bearing or cushion may result in damage to the storage surface from minute dents or scratches. The damage or deformity is caused because of a loading force provided to the transducer to urge it against the disc surface. This loading force is opposed to the force generated by the air bearing effect. The loading force is assigned a value which causes the transducer to come within 12 to 20 microinches of the storage surface during operation.
The storage surfaces may be dented if the transducers are susceptible to the severe complex rotational and/or translational forces sometimes encountered during unusually rough shipping and handling. As disc drives become smaller, and as they move through commerce by common carriers unaccustomed to handling delicate instruments, drives have become susceptible to storage surface damage arising from such severe handling. The most common damage occasioned by severe handling is the denting of the storage surface. Such dents are caused by severe shock forces having substantial components normal to the parallel planes of the disc surfaces. As already mentioned, such dents are known to prevent the drive from storing data at the locations thereof. If such dents occur during shipping and handling between the factory and the user, the presence will go undetected until data storage problems are encountered.
The requirement to lock the data transducer assembly of a rotating rigid disc data storage device during shipment and handling is therefore well recognized in the prior art. Four general approaches have been explored: mechanical locking devices; solenoid safety latches which are disengaged only when the drive is in operation; permanent magnetic latches which lock the assembly against movement in response to shocks below a threshold force level; and air driven safety latches that use the force of the air generated by the rotating disc to disengage the safety latch.
Manual locks are unsatisfactory because they require the intervention of an informed user. If the user is unaware of the manual lock, an attempt to use the drive may result in overload and damage to the transducer actuator. Conversely, the user must remember to engage the manual latch to prevent damage during shipment.
Solenoids are usually effective, but add cost and power consumption overhead. More significantly, they are generally larger than desired. With the progression to smaller form factor disc drives, the size of every component becomes significant.
Permanent magnets are only partially effective. They have the drawback that severe shocks to the drive will overcome the locking force leading to the infliction of the damage sought to be avoided. They also have stray magnetic fields which should be shielded from the disc.
Air driven safety latches have also been shown in the prior art, but typically require significant added time and expense to install, and require multiple parts including biasing springs and the like to maintain the latch in its proper position. Installation requires considerable mechanical skill.
A drawback of Winchester disc drives which must be accounted for is that the unit must be assembled and operated in a very clean, dust-free environment. Once assembled, the disc or discs are enclosed within a hermetically sealed housing to protect against intrusion of unfiltered ambient air. This ultra-clean environment renders impractical the use of most of the locks described above which require a number of rotating or moving parts and can easily lead to the introduction of contaminating particles into the sealed environment through extended use.
A need has therefore arisen to provide a satisfactory locking mechanism which will lock the transducer assembly in a safe position whenever severe mechanical forces or shocks might be encountered, and which will reliably release to enable normal operation of the drive when the storage discs are rotating.